1. Field of the Invention
The present invention relates to a line thermal printer and an energization controlling method thereof. More particularly, the present invention relates to a line thermal printer which makes it possible to perform a controlling operation so that a divided energization process is carried out by easily and properly correcting the temperature loss of heating elements caused by dividing the time of energization with respect to each of the heating elements; and an energization controlling method thereof.
2. Description of the Related Art
Hitherto, there has been known a line thermal printer in which a line thermal head with a length allowing it to oppose the range of printing of a recording medium in a widthwise direction thereof is brought into contact with a platen roller through the recording medium, and, while, in this state of contact, the recording medium is transported as a result of rotationally driving the platen roller, a plurality of heating elements of the line thermal head are selectively driven based on recording information, and generate heat, thereby recording a desired image or the like. The line thermal printer carries out a recording operation by, for example, using a thermosensible paper as a recording medium, and applying heat to the thermosensible paper, or using an ink film, such as an ink ribbon or an ink sheet, and applying heat to the ink film in order to transfer the ink of the ink film onto a recording medium.
The line thermal head of this type of line thermal printer comprises a very large number of heating elements arranged in rows in a direction perpendicular to the direction in which the recording medium is transported. Therefore, when all of the heating elements are energized and driven at the same time, a large drive circuit is required. As a result, the supply power becomes large, so that the heating elements cannot be driven using a battery.
For this reason, there has hitherto been used an energization controlling method which makes it possible to reduce the size of the driving circuit and to drive the heating elements using a battery with a small capacity by energizing every several number of heating elements by dividing the energization process in order to reduce the number of heating elements that are energized at the same time, thereby reducing the amount of applied electrical power.
In the line thermal printer using this type of energization controlling method used to divide the energization process, when a recording operation is being performed on a recording medium, there are times when the heating elements are energized and times when they are not energized. Therefore, when they are not being energized, the heat that has been generated due to the energization of the heating elements that has been previously carried out is radiated, thereby reducing the temperature of the heating elements that are not being energized. In order to decrease the size of the driving circuit and to decrease the amount of applied electrical power, the number of divisions of the energization process with respect to the heating elements must be increased to a certain extent. However, increasing the number of divisions of the energization process with respect to the heating elements causes the time during which the heating elements are energized to be longer than the time during which they are not energized, so that the temperature of the heating elements is reduced even more. In this case, even when the thermal elements are subsequently energized, in performing a recording operation on a recording medium, the temperature may not rise high enough to a recording allowing temperature in order for the heating elements to cause a thermosensible paper to be colored or to cause the ink of an ink film to be transferred onto the recording medium. In that case, the problem that a proper image or the like cannot be recorded on the recording medium arises.
Accordingly, in order for the temperature of each of the heating elements to reach a recording allowing temperature, and a proper recording operation to be performed on the recording medium, it has been necessary to correct the temperature of each of the heating elements.
Here, in correcting the temperature of each of the heating elements, when the numbers of divisions of the energization process with respect to each of the heating elements are different, the times during which energization is not carried out differ, so that heat losses of the heating elements when the next energization of each of the heating elements is carried out differ. Therefore, the temperature of each of the heating elements must be corrected in accordance with the number of divisions of the energization process. Consequently, in correcting the temperatures of the heating elements that differ in accordance with the number of divisions of the energization process, either separate correction factors are provided or correction factors are calculated using a linear functional formula as illustrated in FIG. 6. Here, the correction factor is expressed in accordance with the number of divisions of the energization time required for the temperature of each of the thermal elements to reach the recording allowing temperature.
However, providing separate correction factors that differ in accordance with the number of divisions of the energization process is troublesome because it requires confirmation of the correction factors in accordance with the number of divisions of the energization process.
Through research, the applicant has found out that changes in the temperature of a heating element can be expressed by an exponential functional formula, so that the correction factor used for correcting the temperature loss of the heating element caused by dividing the energization process can be expressed by an exponential functional formula. Therefore, since, when a correction factor is calculated using a linear functional formula, an error occurs between the correction factor and the energization time required for the temperature of each of the heating elements to reach the recording allowing temperature, the problem that a proper recording operation cannot be carried out on a recording medium arises. In addition, in subjecting the heating elements to a divided energization process, the temperature of each of the heating elements and the energization time required for the temperature of each of the heating elements to reach the recording allowing temperature are different in accordance with high and low applied electrical power values. Therefore, since the temperature losses of the heating elements by the time the next energization process is carried out are different, separate correction factors also need to be provided in accordance with high and low applied electrical power values, making it troublesome to provide the correction factors.
Accordingly, in view of the above-described problems, it is an object of the present invention to provide a line thermal printer which makes it possible to perform a controlling operation so that a divided energization process is carried out by easily and properly correcting the temperature losses of heating elements caused by dividing the energization process. It is another object of the present invention to provide an energization controlling method of the line thermal printer.
To this end, according to a first aspect of the present invention, there is provided a line thermal printer in which a plurality of heating elements are disposed at a line thermal head, with the plurality of heating elements being subjected to a divided energization process in order to energize every several number of heating elements by dividing an energization process into a plurality of portions. The line thermal printer comprises controlling means for performing a controlling operation so that the energization of the heating elements is carried out in accordance with an energization time that has been obtained based on a correction factor that has been computed using an exponential functional formula previously provided based on a measured temperature of each of the heating elements.
According to the first aspect, since the correction factor is calculated by the previously provided exponential functional formula, it is not necessary to confirm and to provide the correction factor in accordance with the number of divisions of the energization process and in accordance with high and low electrical power values, so that it is not troublesome to determine the correction factor. In addition, a more accurate correction factor can be determined compared to when the correction factor is computed using a linear functional formula.
According to a second aspect of the present invention, there is provided a line thermal printer in which a plurality of heating elements are disposed at a line thermal head, with the plurality of heating elements being subjected to a divided energization process in order to energize every several number of heating elements by dividing an energization process into a plurality of portions. The line thermal printer comprises controlling means, including a correction factor table which stores correction factors that have been previously computed using a previously provided exponential functional formula, for performing a controlling operation so that the energization of the heating elements is carried out in accordance with an energization time that has been obtained by a correction factor corresponding to a measured temperature of each of the heating elements, obtained from the correction factor table.
According to the second aspect, since the energization time is obtained from the correction factor table which stores the correction factors previously computed using the previously provided exponential functional formula, it is no longer necessary to provide time to compute the correction factor using the exponential functional formula at the controlling means. Therefore, it is possible to easily and properly provide the correction factor, and to quickly provide the correction factor at the controlling means.
According to a third aspect of the present invention, there is provided a method of controlling an energization process in which a controlling operation is carried out so that a plurality of heating elements of a line thermal head are subjected to a divided energization process in order to energize every several number of heating elements by dividing the energization process into a plurality of portions. In the method, a temperature of each of the heating elements is measured, a correction factor is computed using an exponential functional formula that has been previously provided based on the measured temperature of each of the heating elements, and an, energization time is determined based on the computed correction factor in order to subject the heating elements to the divided energization process in accordance with the determined energization time.
According to the third aspect, since the correction factor is calculated by the previously provided exponential functional formula, it is not necessary to confirm and to provide the correction factor in accordance with the number of divisions of the energization process and in accordance with high and low electrical power values, so that it is not troublesome to determine the correction factor. In addition, a more accurate correction factor can be determined compared to when the correction factor is computed using a linear functional formula.
According to a fourth aspect of the present invention, there is provided a method of controlling an energization process in which a controlling operation is carried out so that a plurality of heating elements of a line thermal head are subjected to a divided energization process in order to energize every several number of heating elements by dividing the energization process into a plurality of portions. In the method, a temperature of each of the heating elements is measured, the measured temperature of each of the heating elements and a correction factor that corresponds to the measured temperature of each of the heating elements are obtained from a correction factor table which stores the correction factors that have been previously computed by a previously provided exponential functional formula, and an energization time that corresponds to the obtained correction factor is determined in order to subject the heating elements to the divided energization process for a length of time equal to the determined energization time.
According to the fourth aspect, since the energization time is obtained from the correction factor table that stores the correction factors that have been previously calculated using the previously provided exponential functional formula, it is no longer necessary to provide time for calculating the correction factor using the exponential functional formula when the controlling operation is carried out. Therefore, it is possible to easily and properly provide the correction factor, and to quickly provide the correction factor during the controlling operation.